Difference between Apical and Lateral Meristematic Tissue

According to their main purpose, plant tissues are divided into −

• Meristematic (forming) tissues − ensure the growth of plants;

• Permanent tissues − perform all other functions.

Meristematic cells divide, forming new cells that increase in size and differentiate, forming all plant tissues and organs.

According to their origin, meristematic tissues are divided into primary and secondary.

• Primary meristematic tissues − originate from the seed germ (apical meristems, pericycle);

• Secondary meristematic tissues − originate later in the life of the plant, most often from dedifferentiated parenchyma cells, which regain the ability to divide (cambium, phylogeny).

According to their location, meristematic tissues are divided into

• Apical − located at the tips of the root, their branches. Cause the increase of the roots, stems, and branches in length;

• Lateral − located laterally in the axial organs of the plant. Provide thickening of the root and stem in shrubs, trees, and some herbaceous plants;

• Intercalary − inserted among more or less differentiated tissues. Provide elongation of the plant organs.

What are Apical Meristematic Tissues?

Apical meristematic tissue is a kind of meristematic tissue found at the apical meristem of the root, stem, and their branches, and it is responsible for the elongation of these plant organs. It has a fundamental genesis in the embryonic meristem cells. All flowering plants have this apical meristematic tissue.

To put it another way, the cells that make up the apical meristematic tissue are not all created equal. The protomeristem consists of the first cell or cells, as well as the neighbouring descendant cells. Protomeristem cells can divide indefinitely and keep their meristematic identity right up until the moment the plant dies. Contrary to popular belief, cell division does not occur only in the apical meristematic tissue. It also occurs in primary (transitional) meristems, which are farther away and more poorly differentiated meristematic tissues.

As a result of the work of the apical meristematic tissue, the protoderm, main meristem, and procambia are laid down in concentric cylinders. After remaining meristematic for some time, cells in transitional meristems eventually develop into cells of the ground, vascular, and dermal tissue systems, mostly depending on their position.

Depending on its location, the apical meristematic tissue is −

• Root apical meristematic tissue;

• Stem apical meristematic tissue.

The root apical meristematic tissue forms new cells and contributes to the growth of roots and their branches in length, providing plants with access to water and nutrients.

The stem apical meristematic tissue is located in the apical and lateral buds of the stem and twigs. In addition to forming new cells and increasing the length of the stem and twigs, it also forms −

• Leaf primordia − which develop into leaves;

• Primordia of lateral buds −  which develop into lateral branches.

What are Lateral Meristematic Tissues?

The lateral meristematic tissue is a meristematic tissue located on the lateral side of the stems and roots, causing the growth of plant organs in thickness. They can be of primary or secondary origin.

The lateral meristematic tissue occurs only in trees, shrubs, and some grasses. The lateral meristematic tissues include −

• Cambium;

• Phellogen (cork cambium);

• Procambium;

• Pericycle.

The lateral meristematic tissue forms cylinders located parallel to the long axis of the stems and roots.

The cambium forms the secondary conducting tissues – secondary phloem and secondary xylem. It is a cylinder of several layers of cells – one layer of initial cells and their closest derivatives. It consists of two types of cells −

• Spindle-shaped initial cells − elongated cells, pointed at their ends;

• Ray initial cells − almost isodiametric small cells.

The cells of the cambium divide tangentially. The cells produced outwards from the cambial ring differentiate into cells of the secondary xylem, and those separated inwards – into cells of the secondary phloem.

Cambium cells are secondary in origin and are derived from procambia cells in the conducting bundles and dedifferentiated parenchymal cells located between the conducting bundles.

The phellogen (cork cambium) forms the secondary covering tissue – cork. It is laid the primary bark of the root and stem. The first embedded phylogeny is always a cylinder of several layers of thin-walled cells with a rectangular shape. Its cells divide tangentially and form numerous layers of cortical cells on the outside and several layers of phelloderm cells on the inside. It is with a secondary origin and is derived from dedifferentiated cells of the epidermis or parenchyma of the primary cortex.

The pericycle forms a cylinder of one or more layers of meristem cells, the first layer of the central cylinder of the root. It forms the lateral branches of the root.

Differences: Apical Meristematic Tissue and Lateral Meristematic Tissue

The following table highlights the major differences between Apical Meristematic Tissue and Lateral Meristematic Tissue −

Characteristics	Apical Meristematic Tissue	Lateral Meristematic Tissue
Definition	Apical meristematic tissue is a meristematic tissue located at the top of the root, stem, and their branches, causing the growth of plant organs in length.	The lateral meristematic tissue is a meristematic tissue located on the lateral side of the stems and roots, causing the growth of plant organs in thickness.
Origin	Apical meristematic tissues are of primary origin.	Lateral meristematic tissues are of primary or secondary origin.
Occurrence in plants	Apical meristematic tissue is found in all higher plants.	Lateral meristematic tissue occurs only in trees, shrubs, and some grasses.
Location	Apicalmeristematic tissue is located at the top of the root and stem and their branches.	The lateral meristematic tissue forms cylinders located parallel to the long axis of the stems and roots.
Types	Depending on its location, the apical meristematic tissue is root apical meristematic tissue or stem apical meristematic tissue.	The lateral meristematic tissues are cambium, phellogen (cork cambium), procambium, pericycle.
Growth	The apical meristematic tissue contributes to the growth of roots, stems, and their branches in length, forms primordia of leaves and lateral buds.	The lateral meristematic tissue is responsible for the plant widening/thickening.

Conclusion

The apical meristematic tissue forms the xylem, phloem, epidermis, and ground tissue. In contrast, the lateral meristematic tissue forms wood, inner bark, and outer bark.